1. Field of the Invention
The present invention relates to an apparatus for regenerating information or data from a record thereof which is made by an optical-wave length-multiplexing (hereunder abbriviated as OWM) method.
2. Description of the Prior Art
FIG. 1 shows construction of a prior art apparatus for regenerating information or data from a record thereof made by the OWM method as disclosed in Japanese Patent Publication No. 51,355/83. Further, FIG. 2 illustrates a wavelength spectrum of a medium 1 on which records of information or data have been made by the OWM method.
Referring first to FIG. 1, there are shown a variable wavelength light source 1 such as a semiconductor laser, a controller 2 for regulating the wavelength of light from the light source 1, a collimating lens 3 for focusing light from the light source 1 into a parallel beam, a light deflector 4, an objective lens 5 for converging a beam of light from the light source 1 into a minute spot on a medium 6 on which data can be recorded by the OWM method and which the data can be reproduced from the record thereof, storage elements 7 (each of which is represented by a white circle in this figure) provided on the medium 6 which are properly selected by the light deflector 4, and a photodetector 8 for detecting light which has passed through the storage medium 7.
Next, operation of this apparatus will be described hereinbelow. First, paths of light rays from the light source 1 are collimated by the collimating lens 3 to produce parallel light rays which are then focused by the objective lens 5 into a spot of light which in turn is projected onto a selected one of the storage elements 7 on the medium 6 on which data can be recorded by the OWM method and which the data can be reproduced from the record thereof. The selection of desired one of the storage medium elements 7 is freely conducted by the light deflector 4. With reference to FIG. 2, the principle of the OWM method for recording and reproducing of data will be described hereinbelow. FIG. 2(a) shows an absorption spectrum of such a medium on which a record has not yet been made by the OWM method. As can be seen from this graph, this medium has a wide or broad absorption spectrum. When light having a spectrum (that is, a display of intensity of the light as a function of the wavelength of the light) as indicated by a dotted line in this graph is projected onto this medium, there are produced some drops of intensity of the absorption at the wavelength of the light thus projected, as shown in this figure. These drops of the intensity of the absorption are called "spectral holes" (hereinafter referred to simply as "holes"). When a " hole" is produced, it is supposed that data "1" is recorded at the corresponding wavelength and on the other hand, data "0" is recorded in a region of the wavelength where no "holes" are present. The formation of a hole, that is, the writing of data "1" at a given wavelength can be accomplished by adjusting the wavelength of the light from the source 1 to the given wavelength to be recorded by the use of the wavelength controller 2 and increasing the level of the intensity of the light from the source 1 up to that required for recording of the data or information. The reading of a signal from the medium on which data are recorded by the OWM method as shown in FIG. 2(b) may be effected by scanning the medium by using light of constant intensity from the light source 1 over the range of the wavelength between the upper limit A and the lower limit B of the wavelength used to record the data or information. As shown in FIG. 2(b) which shows an absorption spectrum of the medium onto which the light having the given wavelength is projected, sudden drops or falls in the absorptivity of the medium appear at the wavelengths corresponding to the "holes". Accordingly, the detection of the light, which has passed through the medium 6, effected by the photodetector 8 provides a wavelength spectrum of the medium 6 showing the relation between the intensity and wavelength of the transmitted light as shown in FIG. 2(c). If the medium 6 is scanned over the above described range of the wavelength at a constant rate in time, the photodetector 8 can output a corresponding signal (hereunder sometimes referred to simply as "reproduced signals") which represent information or data to be reproduced and strength of which varies with time.
Being constructed as above described, the prior art apparatus for producing "reproduced signals" from records made by the OWM recording is disadvantageous in that the "reproduced signal" produced from the recorded data do not have constant ground level. Therefore, the "reproduced signal" should be properly processed in such a manner to, for example, keep its ground level constant before being converted into a desired signal representing information.
The present invention is intended to solve the abovementioned problems of the prior art. It is accordingly an object of the present invention to provide an apparatus for regenerating information or data from records made on a medium by the OWM method which can transfer information or data at a high speed.